[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Shutdown panic in disable_nonboot_cpus after cpupool-numa-split
On 28.07.2014 10:50, Jürgen Groß wrote: > On 07/28/2014 10:36 AM, Stefan Bader wrote: >> On 07.07.2014 16:43, Stefan Bader wrote: >>> On 07.07.2014 16:28, Juergen Gross wrote: >>>> On 07/07/2014 04:08 PM, Stefan Bader wrote: >>>>> On 07.07.2014 15:03, Jürgen Groß wrote: >>>>>> On 07/07/2014 02:49 PM, Stefan Bader wrote: >>>>>>> On 07.07.2014 14:38, Jürgen Groß wrote: >>>>>>>> On 07/07/2014 02:00 PM, Andrew Cooper wrote: >>>>>>>>> On 07/07/14 12:33, Stefan Bader wrote: >>>>>>>>>> I recently noticed that I get a panic (rebooting the system) on >>>>>>>>>> shutdown in >>>>>>>>>> some >>>>>>>>> > cases. This happened only on my AMD system and also not all the >>>>>>>>> time. >>>>>>>>> Finally >>>>>>>>> > realized that it is related to the use of using >>>>>>>>> cpupool-numa-split >>>>>>>>> > (libxl with xen-4.4 maybe, but not 100% sure 4.3 as well). >>>>>>>>> > >>>>>>>>> > What happens is that on shutdown the hypervisor runs >>>>>>>>> disable_nonboot_cpus which >>>>>>>>> > call cpu_down for each online cpu. There is a BUG_ON in the >>>>>>>>> code for >>>>>>>>> the case of >>>>>>>>> > cpu_down returning -EBUSY. This happens in my case as soon as >>>>>>>>> the >>>>>>>>> first cpu that >>>>>>>>> > has been moved to pool-1 by cpupool-numa-split is attempted. The >>>>>>>>> error is >>>>>>>>> > returned by running the notifier_call_chain and I suspect that >>>>>>>>> ends >>>>>>>>> up calling >>>>>>>>> > cpupool_cpu_remove which always returns EBUSY for cpus not in >>>>>>>>> pool0. >>>>>>>>> > >>>>>>>>> > I am not sure which end needs to be fixed but looping over all >>>>>>>>> online >>>>>>>>> cpus in >>>>>>>>> > disable_nonboot_cpus sounds plausible. So maybe the check for >>>>>>>>> pool-0 in >>>>>>>>> > cpupool_cpu_remove is wrong...? >>>>>>>>> > >>>>>>>>> > -Stefan >>>>>>>>> >>>>>>>>> Hmm yes - this looks completely broken. >>>>>>>>> >>>>>>>>> cpupool_cpu_remove() only has a single caller which is from >>>>>>>>> cpu_down(), >>>>>>>>> and will unconditionally fail for cpus outside of the default pool. >>>>>>>>> >>>>>>>>> It is not obvious at all how this is supposed to work, and the comment >>>>>>>>> beside cpupool_cpu_remove() doesn't help. >>>>>>>>> >>>>>>>>> Can you try the following (only compile tested) patch, which looks >>>>>>>>> plausibly like it might DTRT. The for_each_cpupool() is a little >>>>>>>>> nastly >>>>>>>>> but there appears to be no cpu_to_cpupool mapping available. >>>>>>>> >>>>>>>> Your patch has the disadvantage to support hot-unplug of the last cpu >>>>>>>> in >>>>>>>> a cpupool. The following should work, however: >>>>>>> >>>>>>> Disadvantage and support sounded a bit confusing. But I think it means >>>>>>> hot-unplugging the last cpu of a pool is bad and should not be working. >>>>>> >>>>>> Correct. >>>>>> >>>>>>> >>>>>>>> >>>>>>>> diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c >>>>>>>> index 4a0e569..73249d3 100644 >>>>>>>> --- a/xen/common/cpupool.c >>>>>>>> +++ b/xen/common/cpupool.c >>>>>>>> @@ -471,12 +471,24 @@ static void cpupool_cpu_add(unsigned int cpu) >>>>>>>> */ >>>>>>>> static int cpupool_cpu_remove(unsigned int cpu) >>>>>>>> { >>>>>>>> - int ret = 0; >>>>>>>> + int ret = -EBUSY; >>>>>>>> + struct cpupool **c; >>>>>>>> >>>>>>>> spin_lock(&cpupool_lock); >>>>>>>> - if ( !cpumask_test_cpu(cpu, cpupool0->cpu_valid)) >>>>>>>> - ret = -EBUSY; >>>>>>>> + if ( cpumask_test_cpu(cpu, cpupool0->cpu_valid) ) >>>>>>>> + ret = 0; >>>>>>>> else >>>>>>>> + { >>>>>>>> + for_each_cpupool(c) >>>>>>>> + { >>>>>>>> + if ( cpumask_test_cpu(cpu, (*c)->cpu_suspended ) ) >>>>>>> >>>>>>> The rest seems to keep the semantics the same as before (though does >>>>>>> that >>>>>>> mean >>>>>>> unplugging the last cpu of pool-0 is ok?) But why testing for suspended >>>>>>> here to >>>>>>> succeed (and not valid)? >>>>>> >>>>>> Testing valid would again enable to remove the last cpu of a cpupool in >>>>>> case of hotplugging. cpu_suspended is set if all cpus are to be removed >>>>>> due to shutdown, suspend to ram/disk, ... >>>>> >>>>> Ah, ok. Thanks for the detail explanation. So I was trying this change in >>>>> parallel and can confirm that it gets rid of the panic on shutdown. But >>>>> when I >>>>> try to offline any cpu in pool1 (if echoing 0 into >>>>> /sys/devices/xen_cpu/xen_cpu? >>>>> is the correct method) I always get EBUSY. IOW I cannot hot-unplug any cpu >>>>> that >>>>> is in a pool other than 0. It does only work after removing it from pool1, >>>>> then >>>>> add it to pool0 and then echo 0 into online. >>>> >>>> That's how it was designed some years ago. I don't want to change the >>>> behavior in the hypervisor. Adding some tool support could make sense, >>>> however. >>> >>> Ok, so in that case everything works as expected and the change fixes the >>> currently broken shutdown and could be properly submitted for inclusion >>> (with my >>> tested-by). >>> >> >> Is this needing something from my side to do? I could re-submit the whole >> patch >> but it since it is Juergen's work it felt a little rude to do so. > > Patch is already in xen-unstable/staging. Argh, so it is. I always seem to forget about this branch. So I only checked master. :/ Thanks, Stefan > > > Juergen > Attachment:
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